Display apparatus capable of adjusting the number of subframes to brightness

ABSTRACT

A display apparatus adjusts the brightness of a plasma display panel. The display apparatus comprises an adjusting device, which acquires image brightness data, and adjusts the number of subfields Z on the basis of brightness data.

TECHNICAL FIELD

The present invention relates to a display apparatus of a plasma displaypanel (PDP) and digital micromirror device (DMD), and more specifically,to a display apparatus capable of adjusting a subfield number inaccordance with brightness.

BACKGROUND ART

A display apparatus of a PDP and a DMD makes use of a subfield method,which has binary memory, and which displays a dynamic image possessinghalf tones by temporally superimposing a plurality of binary images thathave each been weighted. The following explanation deals with PDP, butapplies equally to DMD as well.

A PDP subfield method is explained using FIGS. 1, 2, and 3.

Now, consider a PDP with pixels lined up 10 across and 4 vertically, asshown in FIG. 3. Let the respective R,G,B of each pixel be 8 bits,assume that the brightness thereof is rendered, and that a brightnessrendering of 256 gradations (256 gray scales) is possible. The followingexplanation, unless otherwise stated, deals with a G signal, but theexplanation applies equally to R, B as well.

The portion indicated by A in FIG. 3 has a signal level of brightness of128. If this is displayed in binary, a (1000 0000) signal level is addedto each pixel in the portion indicated by A. Similarly, the portionindicated by B has a brightness of 127, and a (0111 1111) signal levelis added to each pixel. The portion indicated by C has a brightness of126, and a (0111 1110) signal level is added to each pixel. The portionindicated by D has a brightness of 125, and a (0111 1101) signal levelis added to each pixel. The portion indicated by E has a brightness of0, and a (0000 0000) signal level is added to each pixel. Lining up an8-bit signal for each pixel perpendicularly in the location of eachpixel, and horizontally slicing it bit-by-bit produces a subfield. Thatis, in an image display method, which utilizes the so-called subfieldmethod, by which 1 field is divided into a plurality of differentlyweighted binary images, and displayed by temporally superimposing thesebinary images, a subfield is 1 of the divided binary images.

Since each pixel is displayed using 8 bits, as shown in FIG. 2, 8subfields can be achieved Collect the least significant bit of the 8-bitsignal of each pixel, line them up in a 10×4 matrix, and let that besubfield SF1 (FIG. 2). Collect the second bit from the least significantbit, line them up similarly into a matrix, and let this be subfield SF2.Doing this creates subfields SF1, SF2, SF3, SF4, SF5, SF6, SF7, SF8.Needless to say, subfield SF8 is formed by collecting and lining up themost significant bits.

FIG. 4 shows the standard form of a 1 field PDP driving signal. As shownin FIG. 4, there are 8 subfields SF1, SF2, SF3, SF4, SF5, SF6, SF7, SF8in the standard form of a PDP driving signal, and subfields SF1 throughSF8 are processed in order, and all processing is performed within 1field time.

The processing of each subfield is explained using FIG. 4. Theprocessing of each subfield constitutes setup period P1, write period P2and sustain period P3. At setup period P1, a single pulse is applied toa sustaining electrode, and a single pulse is also applied to eachscanning electrode (There are only up to 4 scanning electrodes indicatedin FIG. 4 because there are only 4 scanning lines shown in the examplein FIG. 3, but in reality, there are a plurality of scanning electrodes,480, for example.). In accordance with this, preliminary discharge isperformed.

At write period P2, a horizontal-direction scanning electrodes scanssequentially, and a predetermined write is performed only to a pixelthat received a pulse from a data electrode. For example, whenprocessing subfield SF1, a write is performed for a pixel represented by“1” in subfield SF1 depicted in FIG. 2, and a write is not performed fora pixel represented by “0.”

At sustain period P3, a sustaining pulse (driving pulse) is outputted inaccordance with the weighted value of each subfield. For a written pixelrepresented by “1,” a plasma discharge is performed for each sustainingpulse, and the brightness of a predetermined pixel is achieved with oneplasma discharge. In subfield SF1, since weighting is “1, ” a brightnesslevel of “1” is achieved. In subfield SF2, since weighting is “2,”brightness level of “2” is achieved. That is, write period P2 is thetime when a pixel which is to emit light is selected, and sustain periodP3 is the time when light is emitted a number of times that accords withthe weighting quality.

As shown is FIG. 4, subfields SF1, SF2, SF3, SF4, SF5, SF6, SF7, SF8 areweighted at 1, 2, 4, 8, 16, 32, 64, 128, respectively. Therefore, thebrightness level of each pixel can be adjusted using 256 gradations,from 0 to 255.

In the B region of FIG. 3, light is emitted in subfields SF1, SF2, SF3,SF4, SF5, SF6, SF7, but light is not emitted in subfield SF8. Therefore,a brightness level of “127” (=1+2+4+8+16+32+64) is achieved.

And in the A region of FIG. 3, light is not emitted in subfields SF1,SF2, SF3, SF4, SF5, SF6, SF7, but light is emitted in subfield SF8.Therefore, a brightness level of “128” is achieved.

With the PDP subfield method explained above, to provide an optimumscreen display in bright places and dark places, it is necessary to makeadjustment in accordance with the brightness of an image.

A PDP display apparatus capable of brightness control is disclosed inthe specification of Kokai No. (1996)-286636 (corresponds tospecification in U.S. Pat. No. 5,757,343), but here, only light emissionfrequency and gain control are performed in accordance with brightness,making adequate adjustment impossible.

An object of the present invention is to provide a display apparatuscapable of adjusting a subfield number in accordance with brightness,designed to be able to adjust the number of subfields in accordance withthe brightness of an image (comprising both a dynamic image and a staticimage). The average level of brightness, peak level, PDP powerconsumption, panel temperature, contrast and other factors are used asparameters that represent image brightness.

By increasing the subfield number, it is possible to eliminatepseudo-contour noise, which is explained below, and conversely, bydecreasing the subfield number, although there is the likelihood thatpseudo-contour noise will occur, it is possible to produce a clearerimage.

Pseudo-contour noise is explained below.

Assume that regions A, B, C, D from the state shown in FIG. 3 have beenmoved 1 pixel width to the right as shown in FIG. 5. Thereupon, theviewpoint of the eye of a person looking at the screen also moves to theright so as to follow regions A, B, C, D. Thereupon, 3 vertical pixelsin region B (the B1 portion of FIG. 3) will replace 3 vertical pixels inregion A (A1 portion of FIG. 5) after 1 field. Then, at the point intime when the displayed image changes from FIG. 3 to FIG. 5, the eye ofa human being is cognizant of region B1, which takes the form of alogical product (AND) of B1 region data (01111111) and A1 region data(10000000), that is (00000000). That is, the B1 region is not displayedat the original 127 level of brightness, but rather, is displayed at abrightness level of 0. Thereupon, an apparent dark borderline appears inregion B1. If an apparent change from “1” to “0” is applied to an upperbit like this, an apparent dark borderline appears.

Conversely, when an image changes from FIG. 5 to FIG. 3, at the point intime when it changes to FIG. 3, a viewer is cognizant of region A1,which takes the form of a logical sum (OR) of A1 region data (10000000)and B1 region data (01111111), that is (11111111). That is, the mostsignificant bit is forcibly changed from “0” to “1,” and in accordancewith this, the A1 region is not displayed at the original 128 level ofbrightness, but rather, is displayed at a roughly 2-fold brightnesslevel of 255. Thereupon, an apparent bright borderline appears in regionA1. If an apparent change from “0” to “1” is applied to an upper bitlike this, an apparent bright borderline appears.

In the case of a dynamic image only, a borderline such as this thatappears on a screen is called pseudo-contour noise (“pseudo-contournoise seen in a pulse width modulated motion picture display”:Television Society Technical Report, Vol. 19, No. 2, IDY95-21 pp.61-66), causing degradation of image quality.

DISCLOSURE OF INVENTION

According to the present invention, a display apparatus creates Zsubfields from a first to a Zth. The display apparatus brightens ordarkens the overall image by amplifying a picture signal using amultiplication factor A. The display apparatus performs weighting foreach subfield, outputs a drive pulse of a number N-times this weighting,or outputs a drive pulse of a time length N-times this weighting, andadjusts brightness in accordance with the total drive pulse number ineach pixel, or the total drive pulse time. In the picture signal, thebrightness of each pixel is expressed by Z bits to indicate a particulargradation of the total gradations K. The first subfield is formed bycollecting the 0 and 1 from the entire screen only a first bit of Zbits. The second subfield is formed by collecting the 0 and 1 from theentire screen only a second bit of Z bits. In this manner a first to aZth subfields are formed. The display apparatus adjusts the subfieldnumber in accordance with brightness. To this end, according to thepresent invention, the display apparatus comprises brightness detectingmeans, which acquire image brightness data; and adjusting means, whichadjust the subfield number Z based on brightness data.

According to the present invention, a display apparatus creates, foreach picture, Z subfields from a first to a Zth in accordance with Z bitrepresentation of each pixel, weighting N to each subfield, amultiplication factor A for amplifying a picture signal, and a number ofgradation display points K, said display apparatus comprises:

brightness detecting means, which acquire image brightness data; and

adjusting means, which adjust the subfield number Z based on brightnessdata.

According to a preferred embodiment, said brightness detecting meanscomprises average level detecting means, which detects an average level(Lav) of image brightness.

According to a preferred embodiment, said brightness detecting meanscomprises peak level detecting means, which detects a peak level (Lpk)of image brightness.

According to a preferred embodiment, said brightness detecting meanscomprises power consumption detecting means, which detects the powerconsumption of a display panel on which an image is depicted.

According to a preferred embodiment, said brightness detecting meanscomprises panel temperature detecting means, which detects thetemperature of a display panel on which an image is depicted.

According to a preferred embodiment, said brightness detecting meanscomprises contrast detecting means, which detects the contrast of adisplay panel on which an image is depicted.

According to a preferred embodiment, said brightness detecting meanscomprises ambient illumination detecting means, which detects theperipheral brightness of a display panel on which an image is depicted.

According to a preferred embodiment, the apparatus further comprisesimage characteristic determining means, which generates multiplicationfactor A based on brightness data, and multiplication means, whichamplifies a picture signal A times based on multiplication factor A.

According to a preferred embodiment, the apparatus further comprisesimage characteristic determining means, which generates total number ofgradations K based on brightness data, and display gradation adjustingmeans, which changes a picture signal to the nearest gradation levelbased on total number of gradations K.

According to a preferred embodiment, the apparatus further comprisesimage characteristic determining means, which generates the weighting Nbased on brightness data, and weight setting means, which multipliesN-times the weight of each subfield based on multiple N.

According to a preferred embodiment, said weight setting means is pulsenumber setting means, which sets a drive pulse number.

According to a preferred embodiment, said weight setting means is apulse width setting means, which sets a drive pulse width.

According to a preferred embodiment, the subfield number Z is reduced asthe average level (Lav) of said brightness decreases.

According to a preferred embodiment, the apparatus further comprisesimage characteristic determining means, which generates themultiplication factor A based on brightness data, and multiplying means,which amplifies a picture signal A times based on multiplication factorA, and increases multiplication factor A as the average level (Lav) ofsaid brightness decreases.

According to a preferred embodiment, the apparatus further comprisesimage characteristic determining means, which generates a weightingmultiplier N based on brightness data, and increases a multiplicationresult of multiplication factor A and weighting multiplier N as theaverage level (Lav) of said brightness decreases.

According to a preferred embodiment, the apparatus further comprisesimage characteristic determining means, which generates a weightingmultiplier N based on brightness data, and increases weightingmultiplier N as the average level (Lav) of said brightness decreases.

According to a preferred embodiment, the subfield number Z is increasedas said peak level (Lpk) decreases.

According to a preferred embodiment, the apparatus further comprisingimage characteristic determining means, which generates multiplicationfactor A based on brightness data, and multiplying means, whichamplifies a picture signal A times based on multiplication factor A, andincreases multiplication factor A as said peak level (Lpk) decreases.

According to a preferred embodiment, the apparatus further comprisesimage characteristic determining means, which generates a weightingmultiplier N based on brightness data, and decrease weighting multiplierN as said peak level (Lpk) decreases.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A-1H illustrate a diagram of subfields SF1-SF8.

FIG. 2 illustrates a diagram in which subfields SF1-SF8 overlay oneanother.

FIG. 3 shows a diagram of an example of PDP screen brightnessdistribution.

FIG. 4 shows a waveform diagram showing the standard form of a PDPdriving signal.

FIG. 5 shows a diagram similar to FIG. 3, but particularly showing acase in which 1 pixel moved from the PDP screen brightness distributionof FIG. 3.

FIGS. 6A and 6B show waveform diagrams showing a 1-times mode of a PDPdriving signal with two different subfield numbers.

FIG. 7 shows a waveform diagram showing a 2-times mode of a PDP drivingsignal.

FIG. 8 shows a waveform diagram showing a 3-times mode of a PDP drivingsignal.

FIGS. 9A and 9B show waveform diagrams of standard forms of PDP drivingsignal when number of gradations differ.

FIGS. 10A and 10B show waveform diagrams of PDP driving signal whenvertical synchronizing frequency is 60 Hz and 72 Hz.

FIG. 11 shows a block diagram of a display apparatus of a firstembodiment.

FIG. 12 shows a development schematic map for determining parametersheld in image characteristic determining device 30 in the firstembodiment.

FIG. 13A and 13B show a development schematic map, showing variation ofparameter-determining map shown in FIG. 12.

FIG. 14 shows a block diagram of a display apparatus of a secondembodiment.

FIG. 15 shows a block diagram of a display apparatus of a thirdembodiment.

FIG. 16 shows a block diagram of a display apparatus of a fourthembodiment.

FIG. 17 shows a block diagram of a display apparatus of a fifthembodiment.

FIG. 18 shows a development schematic map, showing a variation of themap shown in FIG. 12.

BEST MODE FOR CARRYING OUT THE INVENTION

Prior to explaining the embodiments of the present invention, a numberof variations of the standard form of a PDP driving signal depicted inFIG. 4 are described.

FIG. 6 (A) shows a standard form PDP driving signal, and FIG. 6 (B)shows a variation of a PDP driving signal, to which 1 subfield has beenadded, and which has subfields SF1 through SF9. For the standard form inFIG. 6 (A), the final subfield SF8 is weighted by 128 sustaining pulses,and for the variation in FIG. 6 (B), each of the last 2 subfields SF8,SF9 are weighted by 64 sustaining pulses. For example, when a brightnesslevel of 130 is to be displayed, with the standard form in FIG. 6 (A),this can be achieved using both subfield SF2 (weighted 2) and subfieldSF8 (weighted 128), whereas with the variation in FIG. 6 (B), thisbrightness level can be achieved using 3 subfields, subfield SF2(weighted 2), subfield SF8 (weighted 64), and subfield SF9 (weighted64). By increasing the number of subfields in this way, it is possibleto decrease the weight of the subfield with the greatest weight.Decreasing the weight like this enables pseudo-contour noise to bedecreased by that much.

FIG. 7 shows a 2-times mode PDP driving signal. Furthermore, the PDPdriving signal shown in FIG. 4 is a 1-times mode. With the 1-times modein FIG. 4, the number of sustaining pulses contained in the sustainperiods P3 for subfields SF1 through SF8, that is, the weighting values,were 1, 2, 4, 8, 16, 32, 64, 128, respectively, but with the 2-timesmode in FIG. 7, the number of sustaining pulses contained in the sustainperiods P3 for subfields SF1 through SF8 are 2, 4, 8, 16, 32, 64, 128,256, respectively, doubling for all subfields. In accordance with this,compared to a standard form PDP driving signal, which is a 1-times mode,a 2-times mode PDP driving signal can produce an image display with 2times the brightness.

FIG. 8 shows a 3-times mode PDP driving signal. Therefore, the number ofsustaining pulses contained in the sustain periods P3 for subfields SF1through SF8 are 3, 6, 12, 24, 48, 96, 192, 384, respectively, triplingfor all subfields.

In this way, although dependent on the degree of margin in 1 field, thetotal number of gradations is 256 gradations, and it is possible tocreate a maximum 6-times mode PDP driving signal. In accordance withthis, it is possible to produce an image display with 6 times thebrightness.

Table 1, Table 2, Table 3, Table 4, Table 5, Table 6 shown below are a1-times mode weighting table, a 2-times mode weighting table, a 3-timesmode weighting table, a 4-times mode weighting table, a 5-times modeweighting table, and a 6-times mode weighting table, respectively, forwhen the subfield number is changed in stages from 8 to 14.

TABLE 1 1-Times Mode Weighting Table Number of Number of Pulses (Weight)in Each Subfield Subfields SF1 SF2 SF3 SF4 SF5 SF6 SF7 SF8 SF9 SF10 SF11SF12 SF13 SF14 Total  8 1 2 4 8 16 32 64 128  — — — — — — 255  9 1 2 4 816 32 64 64 64 — — — — — 255 10 1 2 4 8 16 32 48 48 48 48 — — — — 255 111 2 4 8 16 32 39 39 39 39 36 — — — 255 12 1 2 4 8 16 32 32 32 32 32 3232 — — 255 13 1 2 4 8 16 28 28 28 28 28 28 28 28 — 255 14 1 2 4 8 16 2525 25 25 25 25 25 25 24 255

TABLE 2 2-Times Mode Weighting Table Number of Number of Pulses (Weight)in Each Subfield Subfields SF1 SF2 SF3 SF4 SF5 SF6 SF7 SF8 SF9 SF10 SF11SF12 SF13 SF14 Total  8 2 4 8 16 32 64 128  256  — — — — — — 510  9 2 48 16 32 64 128  128  128  — — — — — 510 10 2 4 8 16 32 64 96 96 96 96 —— — — 510 11 2 4 8 16 32 64 78 78 78 78 72 — — — 510 12 2 4 8 16 32 6464 64 64 64 64 64 — — 510 13 2 4 8 16 32 56 56 56 56 56 56 56 56 — 51014 2 4 8 16 32 50 50 50 50 50 50 50 50 48 510

TABLE 3 3-Times Mode Weighting Table Number of Number of Pulses (Weight)in Each Subfield Subfields SF1 SF2 SF3 SF4 SF5 SF6 SF7 SF8 SF9 SF10 SF11SF12 SF13 SF14 Total  8 3 6 12 24 48 96 192  384  — — — — — — 765  9 3 612 24 48 96 192  192  192  — — — — — 765 10 3 6 12 24 48 96 144  144 144  144  — — — — 765 11 3 6 12 24 48 96 117  117  117  117  108  — — —765 12 3 6 12 24 48 96 96 96 96 96 96 96 — — 765 13 3 6 12 24 48 84 8484 84 84 84 84 84 — 765 14 3 6 12 24 48 75 75 75 75 75 75 75 75 72 765

TABLE 4 4-Times Mode Weighting Table Number of Number of Pulses (Weight)in Each Subfield Subfields SF1 SF2 SF3 SF4 SF5 SF6 SF7 SF8 SF9 SF10 SF11SF12 SF13 SF14 Total  8 4 8 16 32 64 128 256 512 — — — — — — 1020  9 4 816 32 64 128 256 256 256 — — — — — 1020 10 4 8 16 32 64 128 192 192 192192 — — — — 1020 11 4 8 16 32 64 128 156 156 156 156 144 — — — 1020 12 48 16 32 64 128 128 128 128 128 128 128 — — 1020 13 4 8 16 32 64 112 112112 112 112 112 112 112 — 1020 14 4 8 16 32 64 100 100 100 100 100 100100 100 96 1020

TABLE 5 5-Times Mode Weighting Table Number of Number of Pulses (Weight)in Each Subfield Subfields SF1 SF2 SF3 SF4 SF5 SF6 SF7 SF8 SF9 SF10 SF11SF12 SF13 SF14 Total  8 5 10 20 40 80 160 320 640 — — — — — — 1275  9 510 20 40 80 160 320 320 320 — — — — — 1275 10 5 10 20 40 80 160 240 240240 240 — — — — 1275 11 5 10 20 40 80 160 195 195 195 195 180 — — — 127512 5 10 20 40 80 160 160 160 160 160 160 160 — — 1275 13 5 10 20 40 80140 140 140 140 140 140 140 140 — 1275 14 5 10 20 40 80 125 125 125 125125 125 125 125 120 1275

TABLE 6 6-Times Mode Weighting Table Number of Number of Pulses (Weight)in Each Subfield Subfields SF1 SF2 SF3 SF4 SF5 SF6 SF7 SF8 SF9 SF10 SF11SF12 SF13 SF14 Total  8 6 12 24 48 96 192 384 768 — — — — — — 1530  9 612 24 48 96 192 384 384 384 — — — — — 1530 10 6 12 24 48 96 192 288 288288 288 — — — — 1530 11 6 12 24 48 96 192 234 234 234 234 216 — — — 153012 6 12 24 48 96 192 192 192 192 192 192 192 — — 1530 13 6 12 24 48 96168 168 168 168 168 168 168 168 — 1530 14 6 12 24 48 96 150 150 150 150150 150 150 150 144 1530

The way to read these tables is as follows. For example, in Table1-times mode, and when viewing the row, in which the subfield number is12, the table indicates that the weighting of subfields SF1 throughSF12, respectively, are 1, 2, 4, 8, 16, 32, 32, 32, 32, 32, 32, 32. Inaccordance with this, the maximum weight is kept at 32. Further, inTable 3, it is a 3-times mode, and the row in which the subfield numberis 12 constitutes weighting that is 3 times the above-mentioned values,that is, 3, 6, 12, 24, 48, 96, 96, 96, 96, 96, 96.

Table 7, Table 8, Table 9, Table 10, Table 11, Table 12, Table 13 shownbelow indicate which subfield should perform a plasma discharges lightemission in each gradation, when the total number of gradations is 256,then the respective subfield numbers are 8, 9, 10, 11, 12, 13, 14.

TABLE 7 Eight Subfields Gradation/ Subfield No. Number SF1 SF2 SF3 SF4SF5 SF6 SF7 SF8 of Pulses 1 2 4 8 16 32 64 128 0 1 ◯ 2 ◯ 3 ◯ ◯ 4 ◯ 5 ◯ ◯6 ◯ ◯ 7 ◯ ◯ ◯  8-15 Ditto to 0-7 ◯ 16-31 Ditto to 0-15 ◯ 32-63 Ditto to0-31 ◯  64-127 Ditto to 0-63 ◯ 128-255 Ditto to 0-127 ◯ ◯: ActiveSubfield

TABLE 8 Nine Subfields Subfield No. Gradation/ SF1 SF2 SF3 SF4 SF5 SF6SF7 SF8 SF9 Number of Pulses 1 2 4 8 16 32 64 64 64 0 1 ◯ 2 ◯ 3 ◯ ◯ 4 ◯5 ◯ ◯ 6 ◯ ◯ 7 ◯ ◯ ◯  8-15 Ditto to 0-7 ◯ 16-31 Ditto to 0-15 ◯ 32-63Ditto to 0-31 ◯  64-127 Ditto to 0-63 ◯ 128-191 Ditto to 0-63 ◯ ◯192-255 Ditto to 0-63 ◯ ◯ ◯ ◯: Active Subfield

TABLE 9 Ten Subfields Subfield No. Gradation/ SF1 SF2 SF3 SF4 SF5 SF6SF7 SF8 SF9 SF10 Number of Pulses 1 2 4 8 16 32 48 48 48 48 0 2 ◯ 3 ◯ ◯4 ◯ 5 ◯ ◯ 6 ◯ ◯ 7 ◯ ◯ ◯  8-15 Ditto to 0-7 ◯ 16-31 Ditto to 0-15 ◯ 32-63Ditto to 0-31 ◯  64-111 Ditto to 16-63 ◯ 112-159 Ditto to 16-63 ◯ ◯160-207 Ditto to 16-63 ◯ ◯ ◯ 208-255 Ditto to 16-63 ◯ ◯ ◯ ◯ ◯: ActiveSubfield

TABLE 10 Eleven Subfields Subfield No. Gradation/ SF1 SF2 SF3 SF4 SF5SF6 SF7 SF8 SF9 SF10 SF11 Number of Pulses 1 2 4 8 16 32 39 39 39 39 360 1 ◯ 2 ◯ 3 ◯ ◯ 4 ◯ 5 ◯ ◯ 6 ◯ ◯ 7 ◯ ◯ ◯  8-15 Ditto to 0-7 ◯ 16-31 Dittoto 0-15 ◯ 32-63 Ditto to 0-31 ◯  64-102 Ditto to 25-63 ◯ 103-141 Dittoto 25-63 ◯ ◯ 142-180 Ditto to 25-63 ◯ ◯ ◯ 181-244 Ditto to 25-63 ◯ ◯ ◯ ◯245-255 Ditto to 53-63 ◯ ◯ ◯ ◯ ◯ ◯: Active Subfield

TABLE 11 Twelve Subfields Gradation/ Subfield No. Number SF1 SF2 SF3 SF4SF5 SF6 SF7 SF8 SF9 SF10 SF11 SF12 of Pulses 1 2 4 8 16 32 32 32 32 3232 32 0 1 ◯ 2 ◯ 3 ◯ ◯ 4 ◯ 5 ◯ ◯ 6 ◯ ◯ 7 ◯ ◯ ◯  8-15 Ditto to 0-7 ◯ 16-31Ditto to 0-15 ◯ 32-63 Ditto to 0-31 ◯ 64-95 Ditto to 0-31 ◯ ◯  96-127Ditto to 0-31 ◯ ◯ ◯ 128-159 Ditto to 0-31 ◯ ◯ ◯ ◯ 160-191 Ditto to 0-31◯ ◯ ◯ ◯ ◯ 192-223 Ditto to 0-31 ◯ ◯ ◯ ◯ ◯ ◯ 224-255 Ditto to 0-31 ◯ ◯ ◯◯ ◯ ◯ ◯ ◯: Active Subfield

TABLE 12 Thirteen Subfields Gradation/ Subfield No. Number SF1 SF2 SF3SF4 SF5 SF6 SF7 SF8 SF9 SF10 SF11 SF12 SF13 of Pulses 1 2 4 8 16 28 2828 28 28 28 28 28 0 1 ◯ 2 ◯ 3 ◯ ◯ 4 ◯ 5 ◯ ◯ 6 ◯ ◯ 7 ◯ ◯ ◯  8-15 Ditto to0-7 ◯ 16-31 Ditto to 0-15 ◯ 32-59 Ditto to 4-31 ◯ 60-87 Ditto to 4-31 ◯◯  88-115 Ditto to 4-31 ◯ ◯ ◯ 116-143 Ditto to 4-31 ◯ ◯ ◯ ◯ 144-171Ditto to 4-31 ◯ ◯ ◯ ◯ ◯ 172-199 Ditto to 4-31 ◯ ◯ ◯ ◯ ◯ ◯ 200-227 Dittoto 4-31 ◯ ◯ ◯ ◯ ◯ ◯ ◯ 228-255 Ditto to 4-31 ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯: ActiveSubfield

TABLE 13 Fourteen Subfields Gradation/ Subfield No. Number SF1 SF2 SF3SF4 SF5 SF6 SF7 SF8 SF9 SF10 SF11 SF12 SF13 SF14 of Pulses 1 2 4 8 16 2525 25 25 25 25 25 25 24 0 1 ◯ 2 ◯ 3 ◯ ◯ 4 ◯ 5 ◯ ◯ 6 ◯ ◯ 7 ◯ ◯ ◯  8-15Ditto to 0-7 ◯ 16-31 Ditto to 0-15 ◯ 32-56 Ditto to 7-31 ◯ 57-81 Dittoto 7-31 ◯ ◯  82-106 Ditto to 7-31 ◯ ◯ ◯ 107-131 Ditto to 7-31 ◯ ◯ ◯ ◯132-156 Ditto to 7-31 ◯ ◯ ◯ ◯ ◯ 157-181 Ditto to 7-31 ◯ ◯ ◯ ◯ ◯ ◯182-206 Ditto to 7-31 ◯ ◯ ◯ ◯ ◯ ◯ ◯ 207-231 Ditto to 7-31 ◯ ◯ ◯ ◯ ◯ ◯ ◯◯ 232-255 Ditto to 8-31 ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯: Active Subfield

The way to read these tables is as follows. A ◯ indicates an activesubfield. In the active subfield, a plasma discharge light emissionshould be performed to produce a desired gradation level for a certainnoticeable pixel. For example, in the subfield number 12 shown in Table11, since subfields SF2 (weighted 2) and SF3 (weighted 4) can beutilized to produce a level 6 gradation, ◯ is placed in the SF2 and SF3columns. Furthermore, the light-emitting-frequency in subfield SF2 is 2times, and the light-emitting-frequency in subfield SF3 is 4 times, sothat light is emitted a total of 6 times, enabling the production of alevel 6 gradation.

Further, in Table 11, since subfields SF3 (weighted 4), SF6 (weighted32), SF7 (weighted 32), and SF8 (weighted 32) can be utilized to producea level 100 gradation, ◯ is placed in the SF3, SF6, SF7 and SF8 columns.Table 7 through Table 14 show only cases of 1-times mode. For N-timesmode (N is an integer from 1 to 6), a value that is N times the value ofa pulse number can be used.

FIG. 9 (A) shows a standard form PDP driving signal, and FIG. 9 (B)shows a PDP driving signal, when the gradation display points have beenreduced, that is, when the level difference is 2 (when the leveldifference of a standard form is 1). In the case of the standard form inFIG. 9 (A), brightness levels from 0 to 255 can be displayed in 1 pitchusing 256 different gradation display points (0, 1, 2, 3, 4, 5, . . . ,255). In the case of the variation in FIG. 9 (B), brightness levels from0 to 254 can be displayed in 2 pitches using 128 different gradationdisplay points (0, 2, 4, 6, 8, . . . , 254). By enlarging the leveldifference (that is, decreasing the number of gradation display points)in this way without changing the number of subfields, the weight of thesubfield with the greatest weight can be reduced, and as a result,pseudo-contour noise can be reduced.

Table 14, Table 15, Table 16, Table 17, Table 18, Table 19, Table 20shown below are gradation level difference tables for various subfields,and indicate when the number of gradation display points differ.

TABLE 14 Gradation Level Difference Table for Eight Subfields Number ofGrada- tion Display Number of Pulses (Weight) in Each Subfield PointsSF1 SF2 SF3 SF4 SF5 SF6 SF7 SF8 Smax 256 1 2 4  8 16 32 64 128  255 1282 4 8 16 32 64 64 64 254  64 4 8 16  32 48 48 48 48 252

TABLE 15 Gradation Level Difference Table for Nine Subfields Number ofGradation Number of Pulses (Weight) in Each Subfield Display Points SF1SF2 SF3 SF4 SF5 SF5 SF7 SF8 SF9 Smax 256 1 2 4  8 16 32 64 64 64 255 1282 4 8 16 32 48 48 48 48 254  64 4 8 16  32 39 39 39 39 36 252

TABLE 16 Gradation Level Difference Table for Ten Subfields Number ofGradation Number of Pulses (Weight) in Each Subfield Display Points SF1SF2 SF3 SF4 SF5 SF5 SF7 SF8 SF9 SF10 Smax 256 1 2 4  8 16 32 48 48 48 48255 128 2 4 8 16 32 39 39 39 39 36 254  64 4 8 16  32 32 32 32 32 32 32252

TABLE 17 Gradation Level Difference Table for Eleven Subfields Number ofGradation Number of Pulses (Weight) in Each Subfield Display Points SF1SF2 SF3 SF4 SF5 SF5 SF7 SF8 SF9 SF10 SF11 Smax 256 1 2 4  8 16 32 39 3939 39 36 255 128 2 4 8 16 32 32 32 32 32 32 32 254  64 4 8 16  28 28 2828 28 28 28 28 252

TABLE 18 Gradation Level Difference Table for Twelve Subfields Number ofGradation Number of Pulses (Weight) in Each Subfield Display Points SF1SF2 SF3 SF4 SF5 SF5 SF7 SF8 SF9 SF10 SF11 SF12 Smax 256 1 2 4  8 16 3232 32 32 32 32 32 255 128 2 4 8 16 28 28 28 28 28 28 28 28 254  64 4 816  25 25 25 25 25 25 25 25 24 252

TABLE 19 Gradation Level Difference Table for Thirteen Subfields Numberof Gradation Number of Pulses (Weight) in Each Subfield Display PointsSF1 SF2 SF3 SF4 SF5 SF5 SF7 SF8 SF9 SF10 SF11 SF12 SF13 Smax 256 1 2 4 8 16 28 28 28 28 28 28 28 28 255 128 2 4 8 16 25 25 25 25 25 25 25 2524 254  64 4 8 16  23 23 23 23 23 23 23 23 23 17 252

TABLE 20 Gradation Level Difference Table for Fourteen Subfields Numberof Gradation Number of Pulses (Weight) in Each Subfield Display PointsSF1 SF2 SF3 SF4 SF5 SF5 SF7 SF8 SF9 SF10 SF11 SF12 SF13 SF14 Smax 256 12 4  8 16 25 25 25 25 25 25 25 25 24 255 128 2 4 8 16 23 23 23 23 23 2323 23 23 17 254  64 4 8 16  21 21 21 21 21 21 21 21 21 21 14 252

The way to read these tables is as follows. For example, Table 17 is agradation level difference table when the subfield number is 11. Thefirst row shows the weight of each subfield when the number of gradationdisplay points is 256, the second row shows the weight of each subfieldwhen the number of gradation display points is 128, and the third rowshows the weight of each subfield when the number of gradation displaypoints is 64. Smax, the maximum gradation display points that can bedisplayed (that is, the maximum possible brightness level), is indicatedon the right end.

FIG. 10(A) shows a standard form PDP driving signal, and FIG. 10(B)shows a PDP driving signal when the vertical synchronizing frequency ishigh. For an ordinary television signal, the vertical synchronizingfrequency is 60 Hz, but since the vertical synchronizing frequency of apersonal computer or other picture signal has a frequency that is higherthan 60 Hz, for example, 72 Hz, 1 field time becomes substantiallyshorter. Meanwhile, since there is no change in the frequency of thesignal to the scanning electrode or data electrode for driving a PDP,the number of subfields capable of being introduced into a shortened 1field time decreases. FIG. 10 (B) shows a PDP driving signal whensubfields weighted 1 and 2 are eliminated, and the number of subfieldsis 10.

Next, the preferred embodiments are explained. Table 21 shows variousembodiments, and the combination of various characteristics thereof.

TABLE 21 Emb't: Peak Detect Average Detect 1st: x x 2nd: x x (withcontrast detect) 3rd: x x (with ambient illuminance detect) 4th: x x(with power consumption detect) 5th: x x (with panel temperature detect)

First Embodiment

FIG. 11 shows a block diagram of a first embodiment of a displayapparatus capable of adjusting the subfield number in accordance withbrightness. Input 2 receives R, G, B signals. A vertical synchronizingsignal, horizontal synchronizing signal are inputted to a timing pulsegenerator 6 from input terminals VD, HD, respectively. An A/D converter8 receives R, G, B signals and performs A/D conversion. A/D converted R,G, B signals undergo reverse gamma correction via a reverse gammacorrection device 10. Prior to reverse gamma correction, the level ofeach of the R, G, B signals, from a minimum 0 to a maximum 255, isdisplayed in 1 pitch in accordance with an 8-bit signal as 256 linearlydifferent levels (0, 1, 2, 3, 4, 5, . . . , 255). Following reversegamma correction, the levels of the R, G, B signals, from a minimum 0 toa maximum 255, are each displayed with an accuracy of roughly 0.004 inaccordance with a 16-bit signal as 256 non-linearly different levels.

Post-reverse gamma correction R, G, B signals are sent to a 1 fielddelay 11, and are also sent to a peak level detector 26 and an averagelevel detector 28. A 1 field delayed signal from the 1 field delay 11 isapplied to a multiplier 12.

With the peak level detector 26, an R signal peak level Rmax, a G signalpeak level Gmax, and a B signal peak level Bmax are detected in data of1 field, and the peak level Lpk of the Rmax, Gmax and Bmax is alsodetected. That is, with the peak level detector 26, the brightest valuein 1 field is detected. With the average level detector 28, an R signalaverage value Rav, a G signal average value Gav, and a B signal averagevalue Bav are sought in data of 1 field, and the average level Lav ofthe Rav, Gav and Bav is also determined. That is, with the average leveldetector 26, the average value of the brightness in 1 field isdetermined.

An image characteristic determining device 30 receives the average levelLav and peak level Lpk, and decides 4 parameters by combining theaverage level with the peak level: N-times mode value N; multiplicationfactor A of the multiplier 12; number of subfields Z; and number ofgradation display points K.

FIG. 12 is a map for determining parameters used in the firstembodiment. The horizontal axis represents the average level Lav, andthe vertical axis represents the peak level Lpk. Since the peak level isordinarily larger than the average level, the map exists only inside thetriangular area above the 45( diagonal line. The triangular area isdivided by lines parallel to the vertical axis into a plurality ofcolumns, 6 in the case of FIG. 12: C1, C2, C3, C4, C5, C6. Column widthis non-uniform, and becomes wider as the average level increases. Andthe vertical length of the columns is divided by lines parallel to thehorizontal axis, creating a plurality of segments. In column C1, 6segments are formed. In the example in FIG. 12, all together 19 segmentsare formed. The above-mentioned 4 parameters N, A, Z, K are specifiedfor each segment. In FIG. 12, the 4 numerical values depicted insideeach segment indicate the 4 parameters in descending order: N-times modevalue N; multiplication factor A of the multiplier 12; number ofsubfields Z; and number of gradation display points K. The numericalvalues of the 4 parameters are similarly indicated in maps shown inother figures. The segments can be created using another partitioningmethod, and the vertical length of a column can also be divided intosegments that adjust only 1 of the 4 parameters mentioned above.

As is clear from the map in FIG. 12, the lower the average level Lav,the fewer the number of subfields Z. And the lower the peak level, thegreater the number of subfields Z. Further, the lower the average levelLav, the larger the weighting multiplier N. By setting up a map likethis, brightness intensity is emphasized, and, as will be explainedbelow, it is possible to produce a sharp, clear image.

For example, the upper-left segment in FIG. 12 is selected for an image,in which the average level Lav is low, and the peak level Lpk is high.Such an image, for example, might be an image, in which a brightlyshining star is visible in the night sky. In this upper-left segment, a6-times mode is employed, the multiplication factor is set at 1, thenumber of subfields is set at 9, and the number of gradation displaypoints is set at 256. In particular, by setting the weighting multiplierto the 6-times mode, since bright places are highlighted more brightly,a star can be seen as shining more brightly.

Further, the lower-left segment in FIG. 12 is selected for an image, inwhich the average level Lav is low, and the peak level Lpk is low. Suchan image, for example, might be an image of a human form faintly visibleon a dark night. In this lower-left segment, a 1-times mode is employed,the multiplication factor is set at 6, the number of subfields is set at14, and the number of gradation display points is set at 256. Inparticular, by employing the 1-times mode and setting the multiplicationfactor at 6, the gradability of low luminance portions improves, and ahuman form is displayed more clearly.

When the average level is high, since the number of subfields Z can beincreased, and the weighting multiplier N can be decreased, it ispossible to prevent an increase in power consumption and a rise in paneltemperature. Further, by increasing the number of subfields Z, it isalso possible to reduce pseudo-contour lines.

When the average level is low, since the number of subfields can bedecreased, and the number of writes within 1 field time can bedecreased, the temporal margin achieved thereby can be utilized toincrease the weighting multiplier N. Therefore, even dark places can bedisplayed brightly.

When the peak level is high, since the number of subfields Z can be madefewer, and the weighting multiplier N can be increased, artifacts thatshine at peak level in an image, for example, the shining of a star in anight sky, can be highlighted more.

FIG. 13 shows a variation of the map for determining parameters depictedin FIG. 12. Of the 4 parameters, 3 parameters, that is, N-times modevalue N; number of subfields Z; and number of gradation display pointsK, are determined by the map shown in FIG. 13(b), and the remaining oneparameter, that is, the multiplication factor A of the multiplier 12, isdetermined by the map shown in FIG. 13(a). In the map shown in FIG.13(b), the horizontal axis represents the average level Lav, and thevertical axis represents the peak level Lpk. In the map shown in FIG.13(a), the horizontal axis represents the average level Lav, and thevertical axis represents the multiplication factor A. The maps shown inFIG. 13 (a), (b) are both divided into 6 non-uniform (here, the columnwidth widens the larger the average level) columns C1, C2, C3, C4, C5,C6 parallel to the vertical axis.

As is clear from the map shown in FIG. 13(b), the multiplier modes ofthe PDP driving signal in columns C1, C2, C3, C4, C5, C6 become 6-times,5-times, 4-times, 3-times, 2-times, 1-times, respectively. Further, asis clear from the map shown in FIG. 13(a), the multiplication factor Ain each of columns C1, C2, C3, C4, C5, C6 decreases linearly as theaverage level increases. That is, in column C1, it linearly decreasesfrom 1 to ⅚, in column C1, it linearly decreases from 1 to ⅚, in columnC2, it linearly decreases from 1 to ⅘, in column C3, it linearlydecreases from 1 to ¾, in column C4, it linearly decreases from 1 to ⅔,in column C5, it linearly decreases from 1 to ½, in column C6, itlinearly decreases from 1 to ⅓.

When only the map in FIG. 13(b) is utilized, when a certain image ichanges to the next image i+1, if it is assumed, for example, that thedisplay of image i is controlled by the parameters in column C4, and thedisplay of image i+1 is controlled by the parameters in column C5, sincethe PDP driving signal changes from a 3-times mode to a 2-times mode,the image brightness changes gradationally. To correct the gradationalchange of this brightness, the map shown in FIG. 13(a) is used. In theabove example, if it is assumed that the display of image i wasperformed in the vicinity of the right edge of column C4, sincebrightness is proportional to N×A, it would be proportional to 3×⅔=2.Further, if it is assumed that the display of image i1 is performed inthe vicinity of the left edge of column C5, since brightness isproportional to N×A, it would be proportional to 2×1=2. Therefore, bothimage i and image i+1 are driven at a 2-times brightness, and thegradational change of brightness disappears. Further, when the averagelevel of an image is changing in the direction of becoming brighter, forexample, when it is changing from the left edge to the right edge withincolumn C5, PDP drive is performed using a 2-times mode, but because themultiplication factor A changes linearly from 1 to ½, the brightnessalso changes linearly from 2-times.(2×1) to 1-times (2×½).

As is clear from the above, the number of subfields Z is reduced as theaverage level of brightness (Lav) becomes lower. As the average level ofbrightness (Lav) drops, an image darkens, and becomes hard to see. Sincethe weight of a subfield can be enlarged by reducing the number ofsubfields for an image like this, the whole screen can be made brighter.

Further, the number of subfields Z is increased as the peak level ofbrightness (Lpk) becomes lower. When the peak level (Lpk) drops, inaddition to the changing width of the brightness of an image becomingnarrower, the entire image becomes a dark region. By increasing thenumber of subfields Z for an image like this, since the weight of asubfield can be reduced, even if the subfield is moved up or moved down,should a pseudo-contour be generated, it can be kept to a weakpseudo-contour.

Further, the weighting multiplier N is increased as the average level ofbrightness (Lav) becomes lower. As the average level of brightness (Lav)drops, an image darkens, and becomes hard to see. By increasing theweighting multiplier N for an image like this, the whole screen can bemade brighter.

Further, the multiplication factor A is increased as the average levelof brightness (Lav) becomes lower. As the average level of brightness(Lav) drops, an image darkens, and becomes hard to see. By increasingthe multiplication factor A for an image like this, the overall imagecan be made brighter, and gradability can be increased as well.

Further, the weighting multiplier N is decreased as the peak level ofbrightness (Lpk) becomes lower. When the peak level of brightness (Lpk)drops, in addition to the changing width of the brightness of an imagebecoming narrower, the entire image becomes a dark region. By decreasingthe weighting multiplier N for an image like this, the changing width ofthe luminance between display gradations becomes smaller, enabling therendering of fine gradation changes even within the dark image, andmaking it possible to increase gradability.

Further, the multiplication factor A is increased as the peak level ofbrightness (Lpk) becomes lower. When the peak level of brightness (Lpk)drops, in addition to the changing width of the brightness of an imagebecoming narrower, the entire image becomes a dark region. By increasingthe multiplication factor A for an image like this, it becomes possibleto make a distinct change in brightness even when the image is dark, andto increase gradability.

Furthermore, the example given in FIG. 18 can be used as the map fordetermining parameters in the first embodiment. With this map, themultiplication factor A is changed in accordance with the average levelof brightness (Lav) within each segment, and as the average level of-brightness (Lav) becomes lower, the multiplication results of themultiplication factor A and the weighting multiplier N are smoothlyincreased. By so doing, even if the average level of brightness of animage changes while passing between each segment, because themultiplication results of the multiplication factor A and the weightingmultiplier N, which determine image brightness, can be continuouslychanged even at the borders of each segment, it is possible to producean image, in which image brightness smoothly changes.

The image characteristic determining device 30, as explained above,receives the average level (Lav) and peak level (Lpk), and specifies 4parameters N, A, Z, K using a previously-stored map (FIG. 12). Inaddition to using a map, the 4 parameters can also be specified viacalculation and computer processing.

The multiplier 12 receives the multiplication factor A and multipliesthe respective R, G, B signals A times. In accordance with this, theentire screen becomes A-times brighter. Furthermore, the multiplier 12receives a 16-bit signal, which is expressed out to the third decimalplace for the respective R, G, B signals, and after using a prescribedoperation to perform carry processing from a decimal place, themultiplier 12 once again outputs a 16-bit signal.

A display gradation adjusting device 14 receives the number of gradationdisplay points K. The display gradation adjusting device 14 changes thebrightness signal (16-bit), which is expressed in detail out to thethird decimal place, to the nearest gradation display point (8-bit). Forexample, assume the value outputted from the multiplier 12 is 153.125.As an example, if the number of gradation display points K is 128, sincea gradation display point can only take an even number, it changes153.125 to 154, which is the nearest gradation display point. As anotherexample, if the number of gradation display points K is 64, since agradation display point can only take a multiplier of 4, it changes153.125 to 152 (=4×38), which is the nearest gradation display point. Inthis manner, the 16-bit signal received by the display gradationadjusting device 14 is changed to the nearest gradation display point onthe basis of the value of the number of gradation display points K, andthis 16-bit signal is outputted as an 8-bit signal.

A picture signal-subfield corresponding device 16 receives the number ofsubfields Z and the number of gradation display points K, and changesthe 8-bit signal sent from the display gradation adjusting device 14 toa Z-bit signal. As a result of this change, the above-mentioned Table7-Table 20 are stored in the picture signal-subfield correspondingdevice 16. As one example, assume that the signal from the displaygradation adjusting device 14 is 152, for instance, the number ofsubfields Z is 10, and the number of gradation display points K is 256.In this case, in accordance with Table 16, it is clear that the 10-bitweight from the lower bit is 1, 2, 4, 8, 16, 32, 48, 48, 48, 48.Furthermore, by looking at Table 9, the fact that 152 is expressed as(0001111100) can be ascertained from the table. This 10 bits isoutputted to a subfield processor 18. As another example, assume thatthe signal from the display gradation adjusting device 14 is 152, forinstance, the number of subfields Z is 10, and the number of gradationdisplay points K is 64. In this case, in accordance with Table 16, it isclear that the 10-bit weight from the lower bit is 4, 8, 16, 32, 32, 32,32, 32, 32, 32. Furthermore, by looking at the upper 10-bit portion ofTable 11 (Table 11 indicates a number of gradation display points of256, and a subfield number of 12, but the upper 10 bits of this table isthe same as when the number of gradation display points is 64, and thesubfield number is 10), the fact that 152 is expressed as (0111111000)can be ascertained from the table. This 10 bits is outputted to thesubfield processor 18.

The subfield processor 18 receives data from a subfield unit pulsenumber setting device 34, and decides the number of sustaining pulsesput out during sustain period P3. Table 1-Table 6 are stored in thesubfield unit pulse number setting device 34. The subfield unit pulsenumber setting device 34 receives from an image characteristicdetermining device 30 the value of the N-times mode N, the number ofsubfields Z, and the number of gradation display points K, and specifiesthe number of sustaining pulses required in each subfield.

As an example, assume, for instance, that it is the 3-times mode (N=3),the subfield number is 10 (Z=10), and the number of gradation displaypoints is 256 (K=256). In this case, in accordance with Table 3, judgingfrom the row in which the subfield number is 10, sustaining pulses of 3,6, 12, 24, 48, 96, 144, 144, 144, 144 are outputted for each ofsubfields SF1, SF2, SF3, SF4, SF5, SF6, SF&, SF8, SF9, SF10,respectively. In the above-described example, since 152 is expressed as(0001111100), a subfield corresponding to a bit of “1” contributes tolight emission. That is, a light emission equivalent to a sustainingpulse portion of 456 (=24+48+96+144+144) is achieved. This number isexactly equivalent to 3 times 152, and the 3-times mode is executed.

As another example, assume, for instance, that it is the 3-times mode(N=3), the subfield number is 10 (Z=10), and the number of gradationdisplay points is 64 (K=64). In this case, in accordance with Table 3,judging from subfields SF3, SF4, SF5, SF6, SF7, SF8, SF9, SF10, SF11,SF12 of the row in which the subfield number is 12 (The row in Table 3in which the subfield number is 12 has a number of gradation displaypoints of 256, and the subfield number is 12, but the upper 10 bits ofthis row is the same as when the number of gradation display points is64 and the subfield number is 10. Therefore, subfields SF3, SF4, SF5,SF6, SF&, SF8, SF9, SF10, SF11, SF12 of the row in which the subfieldnumber is 12 correspond to subfields SF1, SF2, SF3, SF4, SF5, SF6, SF&,SF8, SF9, SF10 when the subfield number is 10.), sustaining pulses of12, 24, 48, 96, 96, 96, 96, 96, 96, 96 are otuputted for each,respectively. In the above-described example, since 152 is expressed as(0111111000), a subfield corresponding to a bit of “1”contributes tolight emission. That is, a light emission equivalent to a sustainingpulse portion of 456 (=24+48+96+96+96+96+96) is achieved. This number isexactly equivalent to 3 times 152, and the 3-times mode is executed.

In the above-described example, the required number of sustaining pulsescan also be determined via calculations without relying on Table 3, bymultiplying the 10-bit weight obtained in accordance with Table 16 by N(This is 3 times in the case of the 3-times mode.). Therefore, thesubfield unit pulse number setting device 34 can provide an N-timescalculation formula without storing Table 1-Table 6. Further, thesubfield unit pulse number setting device 34 can also set a pulse widthby changing to a pulse number that accords with the type of displaypanel.

Pulse signals required for setup period P1, write period P2 and sustainperiod P3 are applied from the subfield processor 18, and a PDP drivingsignal is outputted. The PDP driving signal is applied to a data driver20, and a scanning/holding/erasing driver 22, and a display is outputtedto a plasma display panel 24.

A vertical synchronizing frequency detector 36 detects a verticalsynchronizing frequency. The vertical synchronizing frequency of anordinary television signal is 60 Hz (standard frequency), but thevertical synchronizing frequency of the picture signal of a personalcomputer or the like is a frequency higher than the standard frequency,for example, 72 Hz. When the vertical synchronizing frequency is 72 Hz,1 field time becomes {fraction (1/72)} second, and is shorter than theordinary {fraction (1/60)} second. However, since the setup pulse,writing pulse and sustaining pulse that comprise a PDP driving signal donot change, the number of subfields that can be introduced into 1 fieldtime decreases. In a case such as this, SF1, which is the leastsignificant bit, is omitted, the number of gradation display point K isset at 128, and an even gradation display point is selected. That is,when the vertical synchronizing frequency detector 36 detects verticalsynchronizing frequency that is higher than a standard frequency, itsends a signal specifying the contents thereof to the imagecharacteristic determining device 30, and the image characteristicdetermining device 30 reduces the number of gradation display points K.Processing similar to that described above is performed for the numberof gradation display points K.

As explained above, in addition to changing the subfield number Z of the4 parameters by combining the average level Lav and the peak level Lpkof 1 field, since it is also possible to change the other parameters:the value of the N-times mode N; the multiplication factor A of themultiplier 12; number of gradation display points K, the highlightingand adjusting of an image can be performed separately in accordance withwhether the image is dark or bright. Further, when an entire image isbright, the brightness can be lowered, and power consumption can also bereduced.

Further, the first embodiment provides a 1 field delay 11, and changesthe rendering form with regard to a 1 field screen, which detects anaverage level Lav and a peak level Lpk, but the 1 field delay 11 can beomitted, and the rendering form can be changed for a 1 field screenfollowing a detected 1 field. Since there is image continuity in adynamic image, this is not particularly problematic because in a certainscene, the detection results are practically the same for an initial 1field and the field thereafter.

Second Embodiment

FIG. 14 shows a block diagram of a display apparatus of a secondembodiment. This embodiment, relative to the embodiment in FIG. 11,further provides a contrast detector 50 parallel to an average leveldetector 28. The image characteristic determining device 30 determinesthe 4 parameters on the basis of image contrast in addition to the peaklevel Lpk and average level Lav, or in place thereof. For example, whencontrast is intense, this embodiment can decrease the multiplicationfactor A.

Third Embodiment

FIG. 15 shows a block diagram of a display apparatus of a thirdembodiment. This embodiment, relative to the embodiment in FIG. 11,further provides an ambient illumination detector 52. The ambientillumination detector 52 receives a signal from ambient illumination 53,outputs a signal corresponding to ambient illumination, and applies thissignal to the image characteristic determining device 30. The imagecharacteristic determining device 30 determines the 4 parameters on thebasis of ambient illumination in addition to the peak level Lpk andaverage level Lav, or in place thereof. For example, when ambientillumination is dark, this embodiment can decrease the multiplicationfactor A, or the weighting multiplier N.

Fourth Embodiment

FIG. 16 shows a block diagram of a display apparatus of a fourthembodiment. This embodiment, relative to the embodiment in FIG. 11,further provides a power consumption detector 54. The power consumptiondetector 54 outputs a signal corresponding to the power consumption ofthe plasma display panel 24, and drivers 20, 22, and applies this signalto the image characteristic determining device 30. The imagecharacteristic determining device 30 determines the 4 parameters on thebasis of the power consumption of the plasma display panel 24 inaddition to the peak level Lpk and average level Lav, or in placethereof. For example, when power consumption is high, the embodiment candecrease the multiplication factor A, or the weighting multiplier N.

Fifth Embodiment

FIG. 17 shows a block diagram of a display apparatus of a fifthembodiment. This embodiment, relative to the embodiment in FIG. 11,further provides a panel temperature detector 56. The panel temperaturedetector 56 outputs a signal corresponding to the temperature of theplasma display panel 24, and applies this signal to the imagecharacteristic determining device 30. The image characteristicdetermining device 30 determines the 4 parameters on the basis of thetemperature of the plasma display panel 24 in addition to the peak levelLpk and average level Lav, or in place thereof. For example, when thetemperature is high, this embodiment can decrease the multiplicationfactor A, or the weighting multiplier N.

As described in detail above, because the display apparatus capable ofadjusting the subfield number in accordance with brightness related tothe present invention adjusts, on the basis of screen brightness data,the number of subfields Z, and also adjusts the value of the N-timesmode N, the multiplication factor A of the multiplier 12, and the valueof the number of gradation display points K, it is capable of creatingof optimum image in accordance with screen brightness. Morespecifically, the advantages of the present invention are as follows.

1) When the average level is low, there is also a margin in panel powerconsumption. When this happens, increasing the weighting multiplier N,and displaying an image brightly enable the reproduction of a beautifulimage with a better contrast-sensation. However, because the number ofsubfields Z was fixed in past driving methods, without being able toadequately set the weighting multiplier N to a sufficiently large value,it was not possible to reproduce a beautiful image with acontrast-sensation. In accordance with the present invention, when theaverage level is low, since a display can be produced by reducing thenumber of subfields Z, it is possible to decrease the number of writesin 1 field time, and by so doing, to enable splitting to increase theweighting multiplier N. By so doing, since the weighting multiplier canbe made sufficiently large, and an image can be made bright, it ispossible to reproduce a beautiful image with a sufficientcontrast-sensation even compared to a CRT or the like. Further, byreducing the number of subfields Z at this time, the pseudo-contournoise generated by a dynamic image worsens, but when the frequency ofimages that generate pseudo-contour noise is not that high, and the typeof image, such as dynamic image, and static image, is comprehensivelydetermined, using the driving method in accordance with the presentinvention enables the reproduction of an extremely beautiful image.

2) When the average level is high, panel power consumption increases.When this happens, if the weighting multiplier N is not decreased, anddisplay is performed without darkening the image, there is a possibilitythat the power consumption of the display device will exceed the ratedpower consumption, and that the panel will be damaged as a result of arise in temperature. However, because the number of subfields Z wasfixed in past driving methods, decreasing the weighting multiplier N hadno other effect than to simply prevent an increase in power consumption,and a rise in panel temperature. In accordance with the presentinvention, when the average level is high, since the subfield number Zcan be increased, and the weighting multiplier N can be decreased, inaddition to preventing an increase in power consumption, and a rise inpanel temperature, the pseudo-contour noise generated by a dynamic imagecan also be reduced. By so doing, when the average level is high, a morebeautiful, stable image than in the past can be reproduced even for adynamic image.

3) When the peak level is low, the number of gradations assigned to anentire picture decreases. In accordance with the present invention,since the multiplication factor A is increased, and the weightingmultiplier N is decreased, the number of gradations assigned to anentire image can be increased. By so doing, since sufficient gradationscan be provided to an entire image, a beautiful image can reproduced,even for an image with a low peak level that is dark overall.

What is claimed is:
 1. A display apparatus for creating, for each image,a number of subfields Z from a first subfield to the Zth subfield inaccordance with a Z bit representation of each pixel, a weight of eachsubfield, and a number of gradation display points, the displayapparatus comprising: an average level detector that detects an averageimage brightness level; an image characteristic determining device thatdetermines a subfield number Z and a weighing multiple, whilemaintaining a same number of gradation display points, based on theaverage image brightness level; and a weight setting device thatmultiplies the weight of each subfield by the weighing multiple; whereinthe image characteristic determining device decreases the subfieldnumber Z and increased the weighing multiple as the average imagebrightness level decreases.
 2. A display apparatus according to claim 1,wherein the image characteristic determining device determines amultiplication factor for amplifying an image signal, based on theaverage image brightness level, the image characteristic determiningdevice comprising a multiplier for amplifying the image signal by themultiplication factor.
 3. A display apparatus according to claim 2,wherein the image characteristic determining device increases themultiplication factor as the average image brightness level decreases.4. A display apparatus according to claim 2, wherein the imagecharacteristic determining device increases a product of themultiplication factor and the weighing multiple as the average imagebrightness level decreases.
 5. A display method for creating, for eachimage, a number of subfields Z from a first subfield to a Zth subfieldin accordance with a Z bit representation of each pixel, a weight ofeach subfield, and a number of gradation display points, the displaymethod comprising: detecting an average image brightness level;determining a subfield number Z and a weighing multiple, whilemaintaining a same number of gradation display points, based on theaverage image brightness level; and multiplying the weight of eachsubfield by the weighing multiple, wherein the subfield number Zdecreases and the weighing multiple increases as the average imagebrightness level decreases.
 6. The display method according to claim 5,wherein the determining determines a multiplication factor foramplifying an image signal, based on the average image brightness level,and the display method further comprising multiplying the image signalby the multiplication factor to amplify the image signal.
 7. The displaymethod according to claim 6, wherein the determining increases themultiplication factor as the average image brightness level decreases.8. The display method according to claim 6, wherein the determiningincreases a product of the multiplication factor and the weighingmultiple as the average image brightness level decreases.